There are many types of stores in which it is desirable to be able to set up an attractive price display on which the prices of articles may be shown, with the names of the articles and their indicated prices being inaccessible to unauthorized persons, but being readily shifted when required. In some cases only a shiftable price display is needed, while in others both the identified articles and the prices need to be changed.
A type of shiftable price display using pre-curled plastic film tapes bearing arabic numerals is disclosed in U.S. Pat. No. 3,939,584. Each of the self-coiling plastic tapes in the device of the patent must be long enough for the individual arabic numerals from 0 through 9 to be displayed separately. This requires a relatively long plastic tape, and restricts the size of the numerals in order to eliminate the need for an excessively long tape. Such a tape for the twenty six letters of the English alphabet is almost prohibitively long.
A number of workers in the prior art have developed apparatus which uses an opaque baseplate with a transparent arabic number 8 on it, in combination with a shiftable mask which cooperates with the arabic number 8 to define any desired arabic numeral from 0 through 9. Various designs of such shiftable masks have been developed which make it possible for the mask to be much smaller than ten times the size of the number 8, because the same opaque and transparent elements may be utilized to form parts of more than one of the numerals. Such mechanisms are illustrated in U.S. Pat. No. 4,047,314 for a digital readout clock; U.S. Pat. No. 3,344,544 for an alpha-numeric display device; U.S. Pat. No. 3,831,303; U.S. Pat. No. 3,444,552 which has characters arranged in a scrambled pattern on a circular surface; and U.S. Pat. No. 3,961,432 which discloses a figure 8 mask much like the one in the present invention. Some of the prior art patents use a single shutter member, while others use multiple shutter members one behind the other.
The prior art includes devices which define numbers or letters by means of transmitted light and others which define them by means of reflected light.
Except for the self coiling tape apparatus, all of the prior art devices are relatively complex and correspondingly expensive.